Carbon and graphite articles have many and diverse applications including use as electrodes, refractories, dies, electrical brushes, structural components in missiles and aircraft, and moderators and reflectors in nuclear reactors. A common method of article fabrication involves mixing a desired blend of carbon particles with a pitch binder; heating the resultant mixture to a sufficiently high temperature to enable the pitch to fluidize the particles; forming the fluidized mixture into a compact; molding or extruding the compact into a desired shape which then is heated to a sufficiently high temperature to coke the pitch; and, if desired, graphitizing the coked articles. During coking the volatile components of the pitch binder vaporize leaving voids in the processed articles. In high performance applications wherein a dense article is required, prior to graphitization the article may be impregnated with additional pitch and rebaked until a desired density is achieved.
High coking value pitches, e.g. pitches having a Modified Conradson Coking Value in excess of about 65 weight percent, generally increase the density and improve the physical properties of carbon and graphite articles. As used herein, Modified Conradson Coking Values refer to carbon yields determined as per the procedure of ASTM test designation D 2416-84. However, high coking value pitches generally have Mettler Softening Points in excess of about 130.degree. C. and thus require the use of relatively high processing temperatures in the mixing and extruding steps of article manufacture. As used herein, Mettler Softening Point refers to the softening point determined as per the procedure of ASTM test designation D 3104-82. High extrusion temperatures are generally undesirable since articles extruded at higher temperatures have a greater tendency to crack during cooling than articles extruded at lower temperatures.
Various additives have been suggested for reducing the softening point of pitch, for example:
U.S. Pat. No. 2,761,848 discloses a process for the production of carbon articles wherein a plasticizer comprising at least one of the materials selected from the group consisting of furfural and furfuryl alcohol is blended with carbon particles and pitch having a melting point not less than 150.degree. C. wherein, the plasticizer to pitch ratio is between about 1 to 3 and 1 to 4; U.S. Pat. No. 3,107,153 discloses a binder comprising pitch and prepolymerized furfuryl alcohol; U.S. Pat. No. 3,171,816 discloses as binder pitch additives, organic compounds selected from the group consisting of vinyl acetate, styrene, phthalodinitrile, acrylonitrile, azobenzene, propargyl alcohol, indene, acenaphthylene, dicyclopentadiene, turpentine oil, divinyl benzene, 1,6-dimorpholinyl-hexadiyne-2, 4, N-.beta.-chlorallyl-morpholine, methacrylic acid, crotonic acid, vinyl proprionate, dibutyl maleate, 1,4-dicyclohexanonyl-diacetylene, 2-butylidene-cyclohexanone-1, acetyl acetone, succinimide, naphthalene dialdehyde, benzil, anthraquinone, cumarinic acid lactone, 2-allyl-oxyanthraquinone, phenyl isocyanate, cyanoacetic acid, malonic acid dinitrile, benzonitrile, adipic acid nitrile, succinodinitrile and benzalaniline.
Similarly, U.S. Pat. No. 3,689,299 discloses the use of furfural, and cyclohexanone or an aliphatic ketone together with a catalyst as pitch binder additives; U.S. Pat. No. 3,840,485 discloses as pitch additives furfural and a member selected from the group consisting of phenol, cyclohexanone and compounds of the formula: EQU CH.sub.3 --CO--R
wherein R is a hydrocarbon group having between 2 and 4 carbon atoms inclusive; and Russian Pat. No. 794,041 discloses the use of vinyl or carbonyl containing furfurylidene-acetone or difurfurylidene acetone oligomers with binder pitch.
While several of the additives previously listed are effective in providing an initial reduction in binder softening points, some of the additives are extremely reactive at typical particle/binder mixing temperatures, e.g. temperatures up to about 160.degree. C. When maintained at such temperatures for a relatively short time such additives may react with pitch to raise the softening point of the binders and increase the viscosity of particle/pitch compositions, resulting in problems in article extrusion. Additionally, whereas some additives are relatively good plasticizers, e.g. effective additives in reducing the softening point of pitch, the additives may have little or no appreciable coking value. The incorporation of additives with extremely low coking values into pitch produces a binder having a coking value significantly less than that of its pitch component. Further, many additives having relatively high coking values are poor plasticizers, being unable to produce binders wherein pitch softening points are significantly reduced.
Accordingly, it is an object of this invention to provide an additive which contributes to the coking value of a binder, reduces the softening points of high softening point pitches to processable temperatures, remains stable at mixing and processing temperatures in excess of about 160.degree. C. and is safely and easily handled at such temperatures. Further objects will be apparent from the ensuing discussion and the appended claims.